JPWO2018150867A1 - Multi-core fiber and multi-core fiber tape using the same - Google Patents

Abstract

The multi-core fiber (1A) includes a plurality of cores (11A) and (11B) arranged in a matrix and a single clad (21) surrounding each of the cores (11A) and (11B). The outer shape of the cross section perpendicular to the longitudinal direction of (21) is a non-circular shape having the smallest diameter in the predetermined direction and no concave portion, and has two or more cores (11A), (11B) along the predetermined direction. ) Are arranged, and a larger number of cores (11A) and (11B) are arranged along the direction perpendicular to the predetermined direction than the number of cores arranged along the predetermined direction, and are bent in the predetermined direction. Used.

Description

  The present invention relates to a multi-core fiber in which many cores can be arranged while suppressing deterioration of long-term reliability.

  An optical fiber used in a widely used optical fiber communication system has a structure in which an outer peripheral surface of one core is surrounded by a clad, and information is transmitted by propagation of an optical signal in the core. The

  In recent years, with the spread of optical fiber communication systems, the amount of information transmitted has increased dramatically. As a means for realizing an increase in transmission capacity of such an optical fiber communication system, a multi-core fiber is known in which the outer peripheral surfaces of a plurality of cores are surrounded by one clad. According to the multi-core fiber, a signal can be transmitted by each light propagating through a plurality of cores, so that the amount of information that can be transmitted by one optical fiber can be increased.

  Patent Document 1 below describes such a multi-core fiber. In this multi-core fiber, a plurality of cores are arranged in one clad. As described in Patent Document 1, in a multi-core fiber, a part of light propagating through mutually adjacent cores may overlap, and crosstalk may occur between the cores. As a method for suppressing the crosstalk, for example, increasing the interval between adjacent cores can be considered. Since crosstalk is determined by the integration of overlap between lights propagating through adjacent cores, crosstalk can be suppressed by increasing the inter-core distance to reduce this overlap. Crosstalk can also be suppressed by a trench structure in which each core is surrounded by a low refractive index layer formed by glass or holes having a lower refractive index than that of the core or cladding. Since the core is surrounded by a low refractive index layer, the spread of light propagating in the core in the radial direction can be reduced, so that the overlap between lights propagating in adjacent cores is reduced and crosstalk is suppressed. Is done.

  Non-Patent Document 1 below describes a single mode in which the bending diameter is 30 mm and the proof level is 1 to 2% in a multi-core fiber actual use environment, the bending diameter is 30 mm and the proof level is 1% and the cladding diameter is 125 μm. The upper limit of the diameter of the clad of the multi-core fiber that is equal to the fiber breaking probability is described as 250 μm.

  In addition, the calculation method of the fracture probability in the bent portion of the optical fiber is described in Non-Patent Document 2 below. This non-patent document 2 has a parameter called maximum bending strain, and this parameter is described in the following non-patent documents 3 and 4.

JP 2012-221964 A

T. Sakamoto, “Low-loss and low-DMD few-mode multi-core fiber with highest core multiplicity factor,” OFC2016, Th5A.2, 2016 Masao Rokuzo, “Mechanical reliability calculation method for bent optical fibers in harsh environments” IEICE Transactions B Vol.J94-B, No.6 pp.738-746 (2011) K. Nagano et al., “Change of the refractive index in an optical fiber due to external forces”, Applied Optics, vol.17, no13, pp.2081-2085 (1978) R. Ulrich et al., “Bending-induced birefringence in single-mode fibers”, Optical Letters, vol.5, no.6, pp.273-275 (1980)

  As described above, when the inter-core distance is increased in order to suppress crosstalk, if a large number of cores are arranged in the cladding, the diameter of the cladding increases. However, optical fibers are often laid in a bent state, and there is a concern that if the diameter of the cladding increases, the probability of breakage increases and long-term reliability deteriorates. Further, when trying to match the fracture probability of the single mode fiber, the diameter of the clad is limited as in Non-Patent Document 1 above.

  Accordingly, an object of the present invention is to provide a multi-core fiber in which a large number of cores can be arranged while suppressing deterioration in long-term reliability, and a multi-core fiber tape using the same.

  In order to solve such a problem, a multi-core fiber of the present invention includes a plurality of cores arranged in a matrix and a single clad surrounding each of the cores, and has an outer shape in a cross section perpendicular to the longitudinal direction of the clad. Is a non-circular shape having the smallest diameter in the predetermined direction and having no recess, and two or more cores are disposed along the predetermined direction and along a direction perpendicular to the predetermined direction. A larger number of cores than the number of cores arranged along the predetermined direction are arranged and bent in the predetermined direction.

  In the case of a conventional multi-core fiber having a circular cross-sectional outer shape of the clad, the upper limit of the number of cores that can be arranged in a predetermined direction is equal to the upper limit of the number of cores that can be arranged in a direction perpendicular to the predetermined direction. However, according to the multi-core fiber of the present invention, for example, the clad cross-sectional area can be made larger than that of a conventional multi-core fiber having a diameter equal to the diameter of the clad of the multi-core fiber of the present invention in a predetermined direction. . In addition, the number of cores arranged along the direction perpendicular to the predetermined direction is larger than the number of cores arranged along the predetermined direction. For this reason, according to the multi-core fiber of the present invention, more cores can be arranged than the conventional multi-core fiber. The multi-core fiber of the present invention is bent in a predetermined direction. That is, the multi-core fiber of the present invention is used by being bent in a predetermined direction. In this case, since the position where the greatest stress is applied to the clad is the position on the outermost peripheral side of the clad in the bent state, the largest stress applied to the clad is the difference between the multi-core fiber of the present invention and the clad of the multi-core fiber of the present invention. The conventional multi-core fiber having a diameter equal to the diameter in the predetermined direction is approximately the same size. Therefore, when the multi-core fiber of the present invention is bent as described above, the breaking probability thereof is substantially equal to the breaking probability of the conventional multi-core fiber. Therefore, according to the multi-core fiber of the present invention, deterioration of long-term reliability can be suppressed.

  In the multi-core fiber, the outer shape of the clad may be a D-type.

  In order to solve this problem, the multi-core fiber tape of the present invention includes a plurality of the above-mentioned multi-core fibers arranged in parallel to each other, and a single tape layer covering each multi-core fiber, and each of the multi-core fibers Are arranged such that the predetermined direction is oriented in a direction perpendicular to the parallel direction of the multi-core fibers.

  In such a multi-core fiber tape, when the tape is bent, each multi-core fiber bends in a predetermined direction. Therefore, it can suppress that the fracture probability of each multi-core fiber deteriorates. Further, a larger number of cores can be arranged by arranging a plurality of multi-core fibers in parallel.

  In order to solve the above problems, a multi-core fiber of the present invention includes a plurality of cores arranged in a matrix and a single clad surrounding each of the cores, and a cross section perpendicular to the longitudinal direction of the clad. The outer shape is an elliptical shape with an ellipticity of 2.5 or less, and two or more cores are arranged along the minor axis direction of the ellipse, and along the minor axis direction along the major axis direction of the ellipse. A larger number of the cores than the number of the cores to be disposed are disposed and bent in a direction of 30 degrees or less with respect to the minor axis direction.

  The present inventors compared the fracture probability of a multi-core fiber with a circular cladding outer shape and the fracture probability of a multi-core fiber with an elliptic cladding outer shape, The conditions for the same break probability were measured with the multi-core fiber. As a result, when a multi-core fiber whose clad outer shape is an ellipse is bent at 30 degrees or less with respect to the minor axis direction, the clad outer shape of each multi-core fiber is more elliptical than a circular multi-core fiber. It has been found that a certain multi-core fiber can have a larger cross-sectional area. Therefore, with such a multi-core fiber, more cores can be arranged while suppressing deterioration in long-term reliability.

  Moreover, in order to solve such a problem, the multi-core fiber tape of the present invention includes a multi-core fiber having an elliptical outer shape of the clad parallel to each other, and a single tape layer covering each multi-core fiber, Each of the multicore fibers is arranged such that the minor axis direction is 30 degrees or less with respect to a direction perpendicular to the parallel direction of the multicore fibers.

  In such a multi-core fiber tape, when the tape is bent, each multi-core fiber bends in a direction of 30 degrees or less with respect to the minor axis direction. Therefore, it can suppress that the fracture probability of each multi-core fiber deteriorates. Further, a larger number of cores can be arranged by arranging a plurality of multi-core fibers in parallel.

  In order to solve the above problems, a multi-core fiber of the present invention includes a plurality of cores arranged in a matrix and a single clad surrounding each of the cores, and a cross section perpendicular to the longitudinal direction of the clad. The outer shape of the racetrack shape is a racetrack shape in which a ratio of a minor axis to a major axis formed by a pair of parallel lines connected by a semicircular curve is 2.5 or less, along the minor axis direction of the racetrack shape. Two or more cores are disposed, and a larger number of cores than the number of cores disposed along the minor axis direction are disposed along the major axis direction of the racetrack shape, It is characterized by being bent in a direction of less than 45 degrees with respect to the direction.

  In such a racetrack shape, the lengths of the respective straight lines are equal to each other, and the diameter is the smallest in the minor axis direction which is a direction perpendicular to the respective straight lines. The present inventors compared the breaking probability of a multi-core fiber having a circular cladding outer shape with the breaking probability of a multi-core fiber having a cladding outer shape having the racetrack shape described above. The conditions under which the same breaking probability was obtained with the multi-core fiber having the racetrack shape as described above were measured. As a result, when the multi-core fiber having the outer shape of the clad having the racetrack shape is bent at less than 45 degrees with respect to the minor axis direction, the outer shape of the clad has a more racetrack shape than the multicore fiber having the circular outer shape. It was found that the cross-sectional area of the multi-core fiber can be increased. Therefore, with such a multi-core fiber, more cores can be arranged while suppressing deterioration in long-term reliability.

  In order to solve such a problem, the multi-core fiber tape of the present invention comprises a multi-core fiber having a track-shaped outer shape of the clad parallel to each other, and a single tape layer covering each multi-core fiber, Each of the multi-core fibers is characterized in that the minor axis direction is arranged at less than 45 degrees with respect to a direction perpendicular to the parallel direction of the multi-core fibers.

  In such a multi-core fiber tape, when the tape is bent, each multi-core fiber bends in a direction of less than 45 degrees with respect to the minor axis direction. Therefore, it can suppress that the fracture probability of each multi-core fiber deteriorates. Further, a larger number of cores can be arranged by arranging a plurality of multi-core fibers in parallel.

  The number of the plurality of cores may be greater than 37.

  As described in Non-Patent Document 1, in a multi-core fiber having a clad having a circular outer shape, if the limit of the diameter of the clad is 250 μm, the number of cores is generally limited to 37. Therefore, the above multi-core fiber is more useful when the number of cores is greater than 37.

  As described above, according to the present invention, it is possible to provide a multicore fiber in which a large number of cores can be arranged while suppressing deterioration in long-term reliability, and a multicore fiber tape using the same.

It is a figure which shows the mode of the external shape of the clad in the cross section perpendicular | vertical to the longitudinal direction of the multi-core fiber in 1st Embodiment of this invention. FIG. 2 is a diagram showing the relationship between the cross-sectional area of a multi-core fiber and the probability of fracture when the ellipticity is 1.5, the bending proof is 1%, and the bending diameter is 60 mm in the multi-core fiber having the clad outer shape shown in FIG. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.0, the bending proof is 1%, and the bending diameter is 60 mm in the multi-core fiber having the cladding outer shape shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.5, the bending proof is 1%, and the bending diameter is 60 mm in the multi-core fiber having the cladding outer shape shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 1.5, the bending proof is 2%, and the bending diameter is 30 mm in the multi-core fiber having the clad outer shape shown in FIG. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.0, the bending proof is 2%, and the bending diameter is 30 mm in the multi-core fiber having the clad outer shape shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.5, the bending proof is 2%, and the bending diameter is 30 mm in the multi-core fiber having the clad outer shape shown in FIG. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the probability of fracture when the ellipticity is 1.5, the bending proof is 2%, and the bending diameter is 60 mm in the multi-core fiber having the cladding outer shape shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.0, the bending proof is 2%, and the bending diameter is 60 mm in the multi-core fiber having the cladding outer shape shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.5, the bending proof is 2%, and the bending diameter is 60 mm in the multi-core fiber having the clad outer shape shown in FIG. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 1.5, the bending proof is 1%, and the bending diameter is 30 mm in the multi-core fiber having the clad outer shape shown in FIG. 1. FIG. 2 is a diagram showing a relationship between a cross-sectional area and a fracture probability when the ellipticity is 2.0, the bending proof is 1%, and the bending diameter is 30 mm in the multi-core fiber having the clad outer shape shown in FIG. 1. FIG. 2 is a diagram showing the relationship between the cross-sectional area and the fracture probability when the ellipticity is 2.5, the bending proof is 1%, and the bending diameter is 30 mm in the multi-core fiber having the cladding outer shape shown in FIG. 1. It is a figure which shows a core element. It is a figure which shows the 1st example of the multi-core fiber in 1st Embodiment. It is a figure which shows the 2nd example of the multi-core fiber in 1st Embodiment. It is a figure which shows the 3rd example of the multi-core fiber in 1st Embodiment. It is a figure which shows the 4th example of the multi-core fiber in 1st Embodiment. It is a figure which shows the 5th example of the multi-core fiber in 1st Embodiment. It is a figure of the 1st form which shows that many cores can be arrange | positioned in the multi-core fiber in 1st Embodiment when angle (theta) is 0 degree | times. It is a figure of the 2nd form which shows that many cores can be arrange | positioned in the multi-core fiber in 1st Embodiment when angle (theta) is 0 degree | times. It is a figure which shows the mode of the external shape of the clad in the cross section perpendicular | vertical to the longitudinal direction of the multi-core fiber in 2nd Embodiment of this invention. In the multi-core fiber having the clad outer shape shown in FIG. 22, the cross-sectional area and the fracture probability of the multi-core fiber when the ratio between the distance between the straight lines and the length of the straight line is 1.5, the bending proof is 1%, and the bending diameter is 60 mm. It is a figure which shows the relationship. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.0, the bending proof is 1%, and the bending diameter is 60 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.5, the bending proof is 1%, and the bending diameter is 60 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 1.5, the bending proof is 2%, and the bending diameter is 30 mm. FIG. In the multi-core fiber having the outer shape of the clad shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.0, the bending proof is 2%, and the bending diameter is 30 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.5, the bending proof is 2%, and the bending diameter is 30 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 1.5, the bending proof is 2%, and the bending diameter is 60 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.0, the bending proof is 2%, and the bending diameter is 60 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.5, the bending proof is 2%, and the bending diameter is 60 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the probability of breakage when the ratio of the distance between the straight lines to the length of the straight line is 1.5, the bending proof is 1%, and the bending diameter is 30 mm. FIG. In the multi-core fiber having the clad outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.0, the bending proof is 1%, and the bending diameter is 30 mm. FIG. In the multi-core fiber having the cladding outer shape shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the ratio between the distance between the straight lines and the length of the straight lines is 2.5, the bending proof is 1%, and the bending diameter is 30 mm. FIG. In a multi-core fiber in which the shape of the clad is a racetrack, it is a diagram showing the relationship between the ratio between the distance between straight lines and the length of the straight lines and the number of cores that can be arranged. It is a figure which shows the 1st example of the multi-core fiber in 2nd Embodiment. It is a figure which shows the 2nd example of the multi-core fiber in 2nd Embodiment. It is a figure which shows the 3rd example of the multi-core fiber in 2nd Embodiment. It is a figure which shows the 4th example of the multi-core fiber in 2nd Embodiment. It is a figure which shows the 5th example of the multi-core fiber in 2nd Embodiment. It is a figure of the 1st form which shows that many cores can be arrange | positioned in the multicore fiber in 2nd Embodiment when angle (theta) is 0 degree | times. It is a figure of the 2nd form which shows that many cores can be arrange | positioned in the multi-core fiber in 2nd Embodiment when angle (theta) is 0 degree | times. It is a figure which shows the multi-core fiber tape in 3rd Embodiment. It is a figure which shows the multi-core fiber tape in 4th Embodiment. It is a figure which shows the other shape of a clad.

  Hereinafter, preferred embodiments of a multi-core fiber according to the present invention will be described in detail with reference to the drawings. For ease of understanding, the scale described in each drawing may be different from the scale described in the following description.

(First embodiment)
FIG. 1 is a diagram showing the appearance of the cladding in a cross section perpendicular to the longitudinal direction of the multi-core fiber in the first embodiment of the present invention. In the drawing, the outer shape of the cladding is shown, and the core and the coating layer are not described. The multi-core fiber of this embodiment is a communication multi-core fiber used for communication.

The clad 21 of the multi-core fiber of the present embodiment has an elliptical cross-sectional shape perpendicular to the longitudinal direction. In the cross section, the clad 21 has a predetermined direction as a minor axis direction and a direction perpendicular to the minor axis direction as a major axis direction. Therefore, the outer shape of the clad 21 is a non-circular shape having the smallest diameter in the predetermined direction and having no recess. Here, as shown in FIG. 1, the size of the minor axis is a, and the size of the major axis is b. In this case, the ellipse is defined by Equation 1 below.

When the ellipticity is e, the ellipticity e is defined by b / a, and when the area of the ellipse that is the area of the clad 21 is S, the area S is defined by the following equation 2.

なお、Ｎ_ｐはプルーフ時の平均破断回数であり、Ｌは曲げターン数が１０回となる実効的な光ファイバの長さであり、ｎは疲労係数であり２０とされ、ｍはワイブルパラメータ(形状指数)であり、ｔ_ｐはプルーフ時間であり１秒とされ、ｔは使用年数であり２０年とされ、σ_ｐはプルーフレベルであり１％または２％とされ、σは最大曲げ歪とされる。Further, according to Non-Patent Document 2, when the fracture probability is F, the fracture probability F is expressed by the following formula 3.

Incidentally, N _p is the average break times during proofing, L is the length of the effective optical fiber count bending turn becomes 10 times, n represents the 20 be the fatigue factor, m is Weibull parameters ( a shape index), t _p is 1 second a proof time, t is the 20 years be age, sigma _p is 1% or 2% be proof level, sigma is the maximum bending strain Is done.

なお、Ｅはガラスのヤング率であり、Ｒ_ｂは曲げ半径であり、ｒは破断確率を求めるマルチコアファイバの座標である。本実施形態では、マルチコアファイバを曲げた場合に最もストレスがかかる部位について求めれば良いので、マルチコアファイバを曲げた際にクラッド２１の最も外側になる位置とした。例えば、マルチコアファイバを短径方向に曲げる場合、座標ｒは（０，ａ／２）となる。According to Non-Patent Documents 3 and 4, the maximum bending strain σ can be approximated by the following formula 4.

E is the Young's modulus of the glass, R _b is the bending radius, and r is the coordinates of the multicore fiber for obtaining the probability of breakage. In the present embodiment, since it is only necessary to obtain a portion that is most stressed when the multi-core fiber is bent, the position is the outermost side of the clad 21 when the multi-core fiber is bent. For example, when a multi-core fiber is bent in the minor axis direction, the coordinate r is (0, a / 2).

  Therefore, in the multi-core fiber having the outer shape of the clad 21 shown in FIG. 1, the relationship between the cross-sectional area and the fracture probability when the multi-core fiber is bent in the direction of the angle θ from the minor axis direction shown in FIG. The single mode fiber is required to have a fracture probability under the condition that the access diameter is 30 mm and the bending diameter is 30 mm. In addition, multi-core fibers with high spatial multiplicity are expected to be used in the trunk line system for long-distance communications, and the probability of breakage may be reduced by setting the bending diameter to 60 mm, or the probability of breakage may be reduced by setting the proof level to 2%. it can.

2-4, the bending proof is 1%, the bending diameter is 60 mm, the ellipticity e is 1.5 in FIG. 2, and in FIG. The calculation was performed with the ellipticity e set to 2.0 and the ellipticity e set to 2.5 in FIG. 5-7, the bending proof is 2%, the bending diameter is 30 mm, the ellipticity e is 1.5 in FIG. 5, and the ellipticity e is FIG. Was calculated with 2.0 as the ellipticity e in FIG. 8 to 10, the bending proof is 2%, the bending diameter is 60 mm, the ellipticity e is 1.5 in FIG. 8, and the ellipticity e is FIG. 9. Was calculated with 2.0 as the ellipticity e in FIG. 11 to 13, the bending proof is 1%, the bending diameter is 30 mm, the ellipticity e is 1.5 in FIG. 11, and the ellipticity e is FIG. The calculation was performed by setting the ellipticity e to 2.5 in FIG. In each figure, the solid line represents the relationship between the cross-sectional area and the breaking probability of the multi-core fiber with the clad having a circular outer shape under the above conditions. Moreover, the horizontal line shown in each figure is a fracture probability when a standard single mode fiber having a cladding diameter of 125 μm is bent at a bending diameter of 30 mm, and its value is 3.2 × 10 ⁻⁶ .

  As shown in FIGS. 2 to 13, if the angle θ from the minor axis direction of the bending direction is 30 degrees or less, the elliptical shape e is 2.5 or less, and the clad shape is elliptical with the same fracture probability. As a result, the cross-sectional area of the multi-core fiber can be made larger than that of the multi-core fiber having a circular cladding shape.

Next, based on the respective calculation results shown in FIGS. 2 to 4, when the angle θ in each figure is 0 degree and 30 degrees, the fracture probability is 3.2 × 10 ^{−6 as} described above. Table 1 shows the cross-sectional area of the clad, the cross-sectional area ratio of the clad having an elliptical cross-sectional shape with respect to the clad having a circular cross-sectional shape, and the minor axis of the clad. However, in Table 1, the minor axis when the cross-sectional shape of the cladding is a circle indicates the diameter of the circle.

Table 2 shows the same items as the items shown in Table 1 based on the calculation results shown in FIGS.

Furthermore, based on the respective calculation results shown in FIGS. 8 to 10, items similar to the items shown in Table 1 are shown in Table 3.

Furthermore, based on the respective calculation results shown in FIGS. 11 to 13, items similar to the items shown in Table 1 are shown in Table 4.

  As described above, when the ellipticity e is 2.5 or less and the angle θ from the minor axis direction of the bending direction is 30 degrees or less, the multi-core fiber having an elliptical clad shape has a clad shape. The cross-sectional area can be made larger than that of a circular multi-core fiber. However, from Table 1 to Table 4, when the ellipticity e is 1.5 or more and 2.0 or less, the cross-sectional area ratio is 1. when the angle θ from the minor axis direction of the bending direction is 0 degree or more and 30 degrees or less. It can be 10 or more. When the ellipticity e exceeds 2.0, the cross-sectional area ratio tends to be smaller than 1.10. Therefore, the ellipticity e is preferably 1.5 or more and 2.5 or less, and more preferably 1.5 or more and 2.0 or less.

  When the angle θ from the minor axis direction in the bending direction is 0 degree, if the ellipticity e is 1.5 or more and 2.5 or less, the cross-sectional area ratio is 1.46 or more and 2.43 or less. In this case, in order to make the cross-sectional area ratio 2 or more, the ellipticity e is preferably 2.0 or more.

  Next, an example of the multi-core fiber of the present embodiment having the clad 21 will be described.

  FIG. 14 is a diagram illustrating core elements, and FIGS. 15 to 19 are diagrams illustrating first to fifth examples of the multi-core fiber according to the present embodiment. The multi-core fibers 1A to 1E in these examples include at least two kinds of core elements 10A, 10B, and 10C arranged in a matrix, and a single elliptical clad 21 surrounding each core element. And the covering layer 30. In each example, the plurality of core elements are of different types from each other. In order to avoid complication of the figure, in the following figures, the core element 10A is indicated by a solid line, the core element 10B is indicated by a broken line, and the core element 10C is indicated by a dotted line.

  As shown in FIG. 14, the core element 10 </ b> A includes a core 11 </ b> A, an inner cladding 12 </ b> A that surrounds the core 11 </ b> A, and a low refractive index layer 13 </ b> A that surrounds the inner cladding 12 </ b> A and is surrounded by the cladding 21. Similarly, the core element 10B includes a core 11B, an inner cladding 12B surrounding the core 11B, and a low refractive index layer 13B surrounding the inner cladding 12B and surrounded by the cladding 21, and the core element 10C includes the core 11C, An inner cladding 12C surrounding the core 11C and a low refractive index layer 13C surrounding the inner cladding 12C and surrounded by the cladding 21 are included. Since the multi-core fibers 1A to 1E have at least two types of core elements among the plurality of core elements 10A, 10B, and 10C arranged in a matrix as described above, the multi-core fibers 1A to 1E are formed in a matrix as described above. And having at least two types of cores among the plurality of cores 11A, 11B, and 11C.

  The cores 11A to 11C have a higher refractive index than the clad 21, the low refractive index layers 13A to 13C have a lower refractive index than the clad 21, and the inner clad 12A is between the core 11A and the low refractive index layer 13A. The inner cladding 12B has a refractive index between the core 11B and the low refractive index layer 13B, and the inner cladding 12C has a refractive index between the core 11C and the low refractive index layer 13C. For example, in the example of FIG. 14, the inner claddings 12 </ b> A to 12 </ b> C have the same refractive index as that of the cladding 21. Thus, each of the core elements 10A to 10C has a trench type refractive index profile. Further, in this embodiment, the refractive index difference with respect to the refractive index of the clad 21 of the core 11A of the core element 10A is the largest, and thus a high refractive index difference core, and the refractive index difference with respect to the refractive index of the clad 21 of the core 11C of the core element 10C. Is the smallest refractive index difference core, and the refractive index difference with respect to the refractive index of the clad 21 of the core 11B of the core element 10B is between the core 11A and the core 11B to be a medium refractive index difference core.

  In the present embodiment, the multi-core fiber shown below has two or more cores arranged along the minor axis direction of the ellipse and cores arranged along the minor axis direction along the major axis direction of the ellipse. More cores than the number are arranged. Further, in the present embodiment, when the axis along the minor axis direction passing through the center of the major axis is the minor axis, the number of cores arranged along the minor axis at a position close to the minor axis is the minor axis. More than the number of cores arranged along the minor axis at a position far from the center.

  In the present embodiment, the cores 11A to 11C are shown as a part of the core elements 10A to 10C, and the clad 21 is connected to the cores 11A to 11C via the inner clads 12A to 12C and the low refractive index layers 13A to 13C. It indirectly surrounds 11C. However, in the present embodiment, the inner claddings 12A to 12C and the low refractive index layers 13A to 13C may be omitted, and the cladding 21 may directly surround the respective cores 11A to 11C.

  A multi-core fiber 1A of the first example shown in FIG. 15 has a clad 21 with an ellipticity e of 1.5, and two types of core elements 10A and 10C are arranged in the clad 21. These core elements 10A and 10C are arranged in a square lattice so that the adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, the array becomes 2-6-8-8-6-2, and the core elements 10A, 10A, The total number of 10C is 32.

In the multi-core fiber 1A of this example, when the proof is 2%, the bending diameter is 30 mm, and the angle θ in the bending direction of the multi-core fiber is 30 degrees, the proof is 1% when the standard single mode fiber is bent at a bending diameter of 30 mm. The cross-sectional area when the fracture probability is the same as the fracture probability of 3.2 × 10 ⁻⁶ is approximately 56.1 × 10 ⁻⁸ μm ² from FIG. Therefore, the minor axis is approximately 218 μm and the major axis is approximately 327 μm. In this case, the distance between the cores can be 28.8 μm. Further, assuming that the ratio of the area occupied by the core elements 10A and 10B to the area surrounded by the outer periphery of the clad 21 is the core exclusive area ratio, the core exclusive area ratio is 37.8%.

  FIG. 16 is a diagram illustrating a second example of the multi-core fiber of the present embodiment. In this example, the multi-core fiber 1B has a clad 21 having an ellipticity e of 1.5, and three types of core elements 10A, 10B, and 10C are arranged in the clad 21. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. In this way, the core elements 10A, 10B, and 10C are arranged in a triangular lattice shape, so that the core elements 10A, 10B, and 10C are arranged in a close-packed form. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, the array becomes 6-9-10-9-6, and the core elements 10A, 10B, The total number of 10C is 40.

The multi-core fiber 1B of this example has the same ellipticity e as the multi-core fiber 1A. Therefore, when the proof is 2%, the bending diameter is 30 mm, and the angle θ in the bending direction of the multi-core fiber is 30 degrees, the fracture probability is 3.2. The cross-sectional area in the case of × 10 ⁻⁶ is approximately 56.0 × 10 ⁻⁸ μm ² from FIG. Therefore, the minor axis is approximately 218 μm and the major axis is approximately 327 μm. Further, the distance between the cores can be 28.8 μm. Further, the core exclusive area ratio is 47.2%.

  FIG. 17 is a diagram illustrating a third example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 1C has a clad 21 having an ellipticity e of 2.0, and three types of core elements 10A, 10B, and 10C are arranged in the clad 21. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, the array becomes 7-10-11-10-7, and the core elements 10A, 10B, The total number of 10C is 41.

In the multi-core fiber 1C of the present example, when the proof is 2%, the bending diameter is 30 mm, and the angle θ in the bending direction of the multi-core fiber is 30 degrees, the cross-sectional area when the fracture probability is 3.2 × 10 ⁻⁶ is FIG. Therefore, it is approximately 56.1 × 10 ⁻⁸ μm ² . Therefore, the major axis is approximately 189 μm and the major axis is approximately 378 μm. Further, the distance between the cores can be 28.8 μm. Moreover, the core occupation area ratio is 48.3%.

Here, Table 5 summarizes the configurations of the multicore fibers 1A to 1C.

Furthermore, the core element 10A~10C of the multicore fiber 1A~ multicore fiber 1C, the refractive index difference with respect to the cladding 21 of the core 11A~11C and delta _1, a refractive index difference with respect to the cladding 21 of low refractive index layer 13A - 13C delta _2, and the radius of the core 11A~11C and _{r 1,} the radius of the outer periphery of the inner cladding 12A~12C and _{r 2,} when the thickness of the low refractive index layer 13A~13C is W, the core element 10A~10C parameters For example, as shown in Table 6 below.

  According to such multi-core fibers 1A to 1C, when the angle θ from the minor axis direction is bent and used in a direction of 30 degrees or less, it has substantially the same reliability as a single mode fiber. Optical communication can be performed.

  FIG. 18 is a diagram illustrating a fourth example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 1D has a clad 21 with an ellipticity e of 1.5, and three types of core elements 10A, 10B, and 10C are arranged in the clad 21. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, the array becomes 6-7-8-7-6, and the core elements 10A, 10B, The total number of 10C is 34.

In the multi-core fiber 1D of this example, when the angle θ in the bending direction of the proof is 1%, the bending diameter is 60 mm, and the multi-core fiber is 30 degrees, the cross-sectional area when the fracture probability is 3.2 × 10 ⁻⁶ is shown in FIG. Therefore, it is approximately 48.8 × 10 ⁻⁸ μm ² . Accordingly, the minor axis is approximately 204 μm and the major axis is approximately 305 μm. Further, the distance between the cores can be 28.8 μm. Moreover, the core occupation area ratio is 52.7%. The parameters of each core element in this example are the same as the parameters of each core element in the second example and the third example.

  FIG. 19 is a diagram illustrating a fifth example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 1E has a clad 21 having an ellipticity e of 2.0, and three types of core elements 10A, 10B, and 10C are arranged in the clad 21. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, the array becomes 6-9-10-9-6, and the core elements 10A, 10B, The total number of 10C is 40.

In the multi-core fiber 1E of this example, when the angle θ in the bending direction of the proof is 1%, the bending diameter is 60 mm, and the multi-core fiber is 30 degrees, the cross-sectional area when the fracture probability is 3.2 × 10 ⁻⁶ is FIG. Therefore, it is approximately 48.8 × 10 ⁻⁸ μm ² . Accordingly, the minor axis is approximately 176 μm and the major axis is approximately 353 μm. Further, the distance between the cores can be 28.8 μm. In addition, the area occupied by the core is 47.4%. The parameters of each core element in this example are the same as the parameters of each core element in the second example and the third example.

Here, Table 7 summarizes the configurations of the multicore fibers 1D to 1E.

  Even when such multi-core fiber 1D to multi-core fiber 1E are used by being bent at an angle θ of 30 degrees or less from the minor axis direction, the optical communication has the same reliability as a single mode fiber. It can be performed.

  In addition, the ellipticity e of the clad 21 and the arrangement of the core elements 10A to 10C shown in the above example are merely examples, and the arrangement of the ellipticity e and the core elements 10A to 10C can be changed as appropriate.

  As described above, the multi-core fibers 1A to 1E of the present embodiment include a plurality of cores 11A to 11C arranged in a matrix and a single clad 21 surrounding each of the cores 11A to 11C. The outer shape in a cross section perpendicular to the longitudinal direction of the clad 21 is an elliptical shape having an ellipticity e of 2.5 or less, two or more cores are disposed along the minor axis direction of the ellipse, and the major axis direction of the ellipse is A larger number of cores are disposed along the minor axis direction. And multicore fiber 1A-1E is bent and used for the direction below 30 degree | times with respect to a minor axis direction.

  Therefore, when the multi-core fibers 1A to 1E having an outer shape of the clad 21 are bent at 30 degrees or less with respect to the minor axis direction and used as described above, The cross-sectional area of the multi-core fibers 1A to 1E having an elliptical outer shape of the clad can be larger than that of the multi-core fiber having a circular outer shape. Therefore, with such multi-core fibers 1A to 1E, more cores can be arranged while suppressing deterioration in long-term reliability.

  Next, it will be described that more cores can be arranged when the angle θ in the direction of bending the multi-core fiber is set to 0 degree.

  FIG. 20 is a diagram of the first embodiment showing that many cores can be arranged in the multicore fiber in the first embodiment when the angle θ is 0 degree. In FIG. 20, the covering layer 30 is omitted. In FIG. 20, the multi-core fiber 101 with a circular cross-sectional shape of the clad, the multi-core fiber 1F with an elliptical cross-sectional shape of the clad and an ellipticity e of 2.0, and an elliptical shape with the elliptical cross-sectional shape of the clad. A multi-core fiber 1G having an e of 2.5 is shown superimposed. That is, in FIG. 20, the multi-core fiber 101 having the circular clad shape and the multi-core fibers 1 </ b> F and 1 </ b> G having the elliptical clad 21 having a short diameter equal to the diameter of the clad of the multi-core fiber 101. It is shown.

  When the multi-core fiber is bent, the most stressed position is the position on the outermost side of the clad in the bent state. Therefore, when the multi-core fibers 1F and 1G having such a cladding are bent at an angle θ from the minor axis direction of 0 degree, the magnitude of the stress at the most stressed position is bent with the same curvature. The magnitude of the stress at the most stressed position in the multi-core fiber 101 is the same. Therefore, when the multi-core fibers 1F and 1G are bent at an angle θ of 0 degrees as described above, the break probability of the multi-core fibers 1F and 1G is equal to the break probability of the multi-core fiber 101 bent with the same curvature. For this reason, compared with the multi-core fiber 101, the multi-core fibers 1F and 1G can suppress deterioration in long-term reliability.

  In addition, as shown in FIG. 20, the short diameter of the clad of the multicore fibers 1F and 1G is the same as the diameter of the clad of the multicore fiber 101 as compared to the multicore fiber 101 having a circular cross-sectional outer shape. It is assumed. Accordingly, the cross-sectional area of the clad of the multi-core fibers 1F and 1G is made larger than the cross-sectional area of the clad of the multi-core fiber 101. In the multi-core fibers 1F and 1G, more core elements are arranged along the major axis direction of the ellipse than the number of core elements arranged along the minor axis direction. Therefore, the multi-core fibers 1F and 1G can have more core elements than the multi-core fiber 101 having the same diameter as the minor axis of the clad of the multi-core fibers 1F and 1G.

  An example of the number of core elements that are specifically arranged will be shown. The core elements that can be disposed in the clad of the multi-core fiber 101 are a core element that overlaps the broken line and a core element that is disposed inside the broken line in FIG. Therefore, the number of core elements included in the multi-core fiber 101 is 37. In addition, the core elements that can be disposed in the clad of the multi-core fiber 1F are a core element that overlaps with a dotted line and a core element that is disposed inside the dotted line in FIG. Accordingly, the number of core elements included in the multi-core fiber 1F is 77. The number of core elements included in the multi-core fiber 1G is 89.

  FIG. 21 is a diagram of the second embodiment showing that many cores can be arranged in the multicore fiber in the first embodiment when the angle θ is 0 degree, as in FIG. 20. In FIG. 20, the multi-core fiber 102 with a circular cross-sectional shape of the clad, the multi-core fiber 1H with an elliptical cross-sectional shape and an ellipticity e of 2.0, and an elliptical shape with an elliptical cross-sectional shape. A multi-core fiber 1I with e of 2.5 is shown superimposed. That is, in FIG. 20, the multi-core fiber 102 having a circular clad shape and the multi-core fibers 1H and 1I each having an elliptical clad 21 having a short diameter equal to the diameter of the clad of the multi-core fiber 102 are shown. It is shown.

  Similarly to the description in FIG. 20, when the multi-core fibers 1H and 1I are bent at an angle θ from the minor axis direction of 0 degree, the break probability of the multi-core fibers 1H and 1I is the multi-core fiber 102 bent with the same curvature. Is made equal to the probability of breakage. Therefore, the multi-core fibers 1H and 1I can suppress deterioration in long-term reliability as compared with the multi-core fiber 102.

  Similarly to the description in FIG. 20, the cross-sectional area of the clad of the multi-core fibers 1H and 1I is made larger than the cross-sectional area of the clad of the multi-core fiber 102. In the multi-core fibers 1H and 1I, along the major axis direction of the ellipse. More core elements than the number of core elements arranged along the minor axis direction are arranged. Therefore, the multi-core fibers 1H and 1I can have more core elements than the multi-core fiber 102 having the same diameter as the minor axis of the clad of the multi-core fibers 1H and 1I.

  An example of the number of core elements that are specifically arranged will be shown. In FIG. 21, core elements that can be arranged in the clad of the multi-core fiber 102 are core elements that overlap the broken line and core elements that are arranged inside the broken line, and the number of core elements that the multi-core fiber 102 has is 37. In FIG. 21, the core elements that can be arranged in the clad of the multi-core fiber 1H are the core elements that overlap with the dotted line and the core elements that are arranged inside the dotted line, and the number of core elements that the multi-core fiber 1H has is 89. The The number of core elements included in the multi-core fiber 1I is 105.

  As described above, the multi-core fiber of the present embodiment includes a plurality of cores 11A to 11C arranged in a matrix and a single clad 21 surrounding each of the cores 11A to 11C. The outer shape in a cross section perpendicular to the longitudinal direction of the clad 21 is a non-circular shape having the smallest diameter in the predetermined direction and having no recess. Two or more cores 11A to 11C are arranged along a predetermined direction, and more cores are arranged along a direction perpendicular to the predetermined direction than the number of cores arranged along the predetermined direction. Are bent in a predetermined direction.

  As described with reference to FIGS. 20 and 21, in the case of the conventional multi-core fibers 101 and 102 in which the outer shape of the cladding is circular, the upper limit of the number of cores that can be arranged in a predetermined direction is perpendicular to the predetermined direction. The upper limit of the number of cores that can be arranged in the direction is equal to each other. However, according to the multi-core fibers 1F to 1I of the present embodiment, for example, from the conventional multi-core fibers 101 and 102 having a diameter equal to the diameter of the minor axis direction which is a predetermined direction of the cladding of the multi-core fibers 1F to 1I of the present embodiment. However, the cross-sectional area of the cladding can be increased. And the number of cores 11A-11C arrange | positioned along the direction perpendicular | vertical to a predetermined direction is increased rather than the number of cores 11A-11C arrange | positioned along a predetermined direction. For this reason, according to the multi-core fibers 1F to 1I of the present embodiment, more cores than the conventional multi-core fibers 101 and 102 can be arranged. Further, the multi-core fibers 1F to 1I of the present embodiment are used by being bent in a predetermined direction. In this case, since the position where the largest stress is applied to the clad is the position on the outermost peripheral side of the clad 21 in the bent state, the largest stress applied to the clad is the multi-core fibers 1F to 1I of the present embodiment and the conventional multi-core. The fibers 101 and 102 have substantially the same size. Therefore, when the multi-core fibers 1F to 1I according to the present invention are bent as described above, the break probability thereof is substantially equal to the break probability of the conventional multi-core fibers 101 and 102. Therefore, according to the multi-core fibers 1F to 1I of the present invention, deterioration of long-term reliability can be suppressed.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to FIGS. In addition, about the component which is the same as that of 1st Embodiment, or equivalent, except the case where it demonstrates especially, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 22 is a diagram showing the outer shape of the clad in a cross section perpendicular to the longitudinal direction of the multi-core fiber in the second embodiment of the present invention. In the drawing, the outer shape of the cladding is shown, and the core and the coating layer are not described. In addition, the multi-core fiber of the present embodiment is a communication multi-core fiber used for communication in the same manner as the multi-core fiber of the first embodiment.

  The clad 22 of the multi-core fiber of this embodiment has a cross-sectional shape perpendicular to the longitudinal direction and a racetrack shape in which a set of straight lines 22L parallel to each other are connected by a semicircular curve 22C. The respective straight lines 22L are in a relationship of being translated from each other. Further, in this cross section, the direction perpendicular to the straight line 22L is the minor axis direction and the direction along the straight line 22L is the major axis direction in the cross section. When this minor axis direction is a predetermined direction, the outer shape of the clad 22 is a non-circular shape having the smallest diameter in the predetermined direction and having no recess. Here, as shown in FIG. 22, the short diameter which is the distance between the straight lines 22L is a, and the long diameter is b. Here, in this embodiment, the ratio (b / a) between the minor axis a and the major axis b is assumed to be e.

  Also in the case of the clad 22 of this embodiment, the breaking probability of the multi-core fiber is expressed by Equation 3. Therefore, in the multi-core fiber having the outer shape of the clad 22 shown in FIG. 22, the relationship between the cross-sectional area and the fracture probability when the multi-core fiber is bent in the direction of the angle θ from the minor axis direction shown in FIG. It calculated | required considering the same thing as the time of calculating | requiring a fracture | rupture probability.

23 to FIG. 25, the bending proof is 1%, the bending diameter is 60 mm, the ratio e is 1.5 in FIG. 23, and the ratio e is 2.0 in FIG. In FIG. 25, the calculation was performed with the ratio e set to 2.5. Further, in the relationship between the cross-sectional area and the fracture probability shown in FIGS. 26 to 28, the bending proof is 2%, the bending diameter is 30 mm, the ratio e is 1.5 in FIG. 26, and the ratio e is 2 in FIG. The calculation was performed by setting the ratio e to 2.5 in FIG. 29-31, the bending proof is 2%, the bending diameter is 60 mm, the ratio e is 1.5 in FIG. 29, and the ratio e is 2 in FIG. The calculation was performed by setting the ratio e to 2.5 in FIG. 32 to 34, the bending proof is 1%, the bending diameter is 30 mm, the ratio e is 1.5 in FIG. 32, and the ratio e is 2 in FIG. The calculation was performed with a ratio e of 2.5 in FIG. 2 to 13 of the first embodiment, in each drawing, a solid line indicates the relationship between the cross-sectional area and the breaking probability of the multi-core fiber having a circular clad outer shape under the above conditions. Similarly to FIGS. 2 to 13 of the first embodiment, the horizontal line shown in each figure is the probability of breakage when a standard single mode fiber having a cladding diameter of 125 μm is bent at a bending diameter of 30 mm, and the value Is 3.2 × 10 ⁻⁶ .

  As shown in FIGS. 23 to 34, if the angle θ from the minor axis direction of the bending direction is less than 45 degrees, the ratio e of the minor axis a to the major axis b is 2.5 or less, and the same breaking probability is obtained. As a result, the cross-sectional area of the multi-core fiber with the racetrack shape of the clad can be larger than that of the multi-core fiber with the circular shape of the clad.

Next, based on the respective calculation results shown in FIG. 23 to FIG. 25, the fracture probability is 3.2 × 10 ⁻⁶ when the angle θ in each figure is 0 degree, 30 degrees, and 45 degrees. Table 8 shows the cross-sectional area of the clad, the cross-sectional area ratio of the clad whose cross-sectional shape is a racetrack shape, and the minor axis of the clad. However, in Table 8, the minor axis when the cross-sectional shape of the cladding is a circle indicates the diameter of the circle.

In addition, based on the respective calculation results shown in FIGS. 26 to 28, items similar to the items shown in Table 8 are shown in Table 9.

Furthermore, based on the respective calculation results shown in FIGS. 29 to 31, items similar to the items shown in Table 8 are shown in Table 10.

Furthermore, based on the respective calculation results shown in FIG. 32 to FIG. 34, items similar to the items shown in Table 8 are shown in Table 11.

  As described above, when the ratio e between the minor axis a and the major axis b is 2.5, if the angle θ from the minor axis direction in the bending direction is 30 degrees or less, the shape of the clad is a racetrack-shaped multicore fiber. However, the cross-sectional area can be made larger than that of a multi-core fiber having a circular cladding shape. When the angle θ is 45 degrees, the cross-sectional area of the multicore fiber having the racetrack shape of the clad may be slightly smaller than the circular multicore fiber at the ratio e of 1.5. However, in this case, the cross-sectional area of the racetrack-shaped multicore fiber is substantially the same as that of the circular multicore fiber. Therefore, if the angle θ is less than 45 degrees, the cross-sectional area of the multicore fiber with the racetrack shape of the clad can be larger than that of the multicore fiber with the circular shape of the clad. In particular, when the angle θ is 44 degrees or less, the cross-sectional area of the multicore fiber having a racetrack shape of the clad can be more reliably increased than the multicore fiber having a circular clad shape. Furthermore, if the ratio e is 2.0 or more and 2.5 or less, the cross-sectional area of the multicore fiber with the racetrack shape of the clad is smaller than that of the circular multicore fiber when the angle θ is 45 degrees or less. This is preferable because there is not.

  Here, in FIG. 35, in the multi-core fiber in which the shape of the clad 22 is a racetrack shape as in this embodiment, the relationship between the ratio e between the short diameter a and the long diameter b and the number of cores that can be arranged is shown. . FIG. 35 shows the ratio e and the cross-sectional area obtained by fixing the minor axis a which is the distance between the straight lines and changing the major axis b, and the core elements 10A to 10C described in Table 6 are used. The number obtained by dividing the cross-sectional area by the area is the number of cores. As shown in FIG. 35, it can be seen that the larger the ratio e, the larger the number of cores that can be arranged, when the ratio e is at least 2.5, regardless of the minor axis a.

  Next, an example of the multi-core fiber of the present embodiment having the cladding 22 will be described.

  In the multi-core fiber of the present embodiment having such a clad 22, for example, the core elements 10A to 10C shown in FIGS. Also in the present embodiment, the inner claddings 12A to 12C and the low refractive index layers 13A to 13C may be omitted, and the cladding 22 may directly surround the respective cores 11A to 11C.

  In the present embodiment, in the multi-core fiber shown below, two or more cores are arranged along the minor axis direction of the racetrack shape, and are arranged along the minor axis direction along the major axis direction of the race track shape. More cores than the number of cores are arranged. Further, in the present embodiment, when the axis along the minor axis direction passing through the center of the major axis is the minor axis, the number of cores arranged along the minor axis at a position close to the minor axis is the minor axis. More than the number of cores arranged along the minor axis at a position far from the center.

A multi-core fiber 2A of the first example shown in FIG. 36 has a clad 22 having a ratio e of a minor axis a to a major axis b of 1.5, and two types of cores 10A and 10C in the clad 22 Elements are arranged in a square lattice so as to be of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, an array of 4-6-8-8-6-4 is obtained, and the core elements 10A, 10A, The total number of 10C is 36. 2. In the multi-core fiber 2A of this example, assuming that the proof is 1%, the bending diameter is 60 mm, and the angle θ in the bending direction of the multi-core fiber is 30 degrees, the breaking probability when the standard single-mode fiber is bent with a bending diameter of 30 mm. The cross-sectional area when the fracture probability is the same as 2 × 10 ⁻⁶ is approximately 52.8 × 10 ⁻⁸ μm ² from FIG. Therefore, the minor axis is approximately 202.7 μm, and the major axis is approximately 304.1 μm. In this case, the distance between the cores can be 28.8 μm. Further, assuming that the ratio of the area occupied by the core elements 10A and 10B to the area surrounded by the outer periphery of the clad 21 is the core exclusive area ratio, the core exclusive area ratio is 44.4%.

FIG. 37 is a diagram illustrating a second example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 2B has a clad 22 having a ratio e of the minor axis a to the major axis b of 1.5, and three types of core elements 10A, 10B, and 10C are arranged in the clad 22. Has been. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. In this way, the core elements 10A, 10B, and 10C are arranged in a triangular lattice shape, so that the core elements 10A, 10B, and 10C are arranged in a close-packed form. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, the array becomes 6-7-8-7-6, and the core elements 10A, 10B, The total number of 10C is 34. 2. In the multi-core fiber 2B of this example, assuming that the proof is 1%, the bending diameter is 60 mm, and the angle θ in the bending direction of the multi-core fiber is 30 degrees, the breaking probability when the standard single mode fiber is bent with a bending diameter of 30 mm. The cross-sectional area when the fracture probability is the same as 2 × 10 ⁻⁶ is approximately 52.8 × 10 ⁻⁸ μm ² from FIG. Therefore, the minor axis is approximately 202.7 μm, and the major axis is approximately 304.1 μm. In this case, the distance between the cores can be 28.8 μm. Further, assuming that the ratio of the area occupied by the core elements 10A, 10B, and 10C to the area surrounded by the outer periphery of the clad 21 is the core exclusive area ratio, the core exclusive area ratio is 41.9%.

FIG. 38 is a diagram illustrating a third example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 2C has a clad 22 having a ratio e of 2.0, and three types of core elements 10A, 10B, and 10C are arranged in the clad 22. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, an array of 7-8-9-8-7 is obtained, and the core elements 10A, 10B, The total number of 10C is 39. 2. In the multi-core fiber 2C of this example, assuming that the proof is 1%, the bending diameter is 60 mm, and the angle θ in the bending direction of the multi-core fiber is 45 degrees, the probability of breakage when the standard single-mode fiber is bent with a bending diameter of 30 mm. The cross-sectional area when the fracture probability is the same as 2 × 10 ⁻⁶ is approximately 48.6 × 10 ⁻⁸ μm ² from FIG. Accordingly, the minor axis is approximately 165.0 μm and the major axis is approximately 330.0 μm. In this case, the distance between the cores can be 28.8 μm. Further, assuming that the ratio of the area occupied by the core elements 10A, 10B, and 10C to the area surrounded by the outer periphery of the clad 21 is the core exclusive area ratio, the core exclusive area ratio is 52.2%.

FIG. 39 is a diagram illustrating a fourth example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 2D has a clad 22 with a ratio e of 1.5, and three types of core elements 10A, 10B, and 10C are arranged in the clad 22. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, an array of 5-6-7-8-7-6-5 is obtained. The total number of 10A, 10B, and 10C is 44. 2. In the multi-core fiber 2D of this example, the probability of breakage when the standard single mode fiber is bent at a bending diameter of 30 mm when the proof is 2%, the bending diameter is 30 mm, and the angle θ in the bending direction of the multi-core fiber is 30 degrees. The cross-sectional area when the fracture probability is the same as 2 × 10 ⁻⁶ is approximately 60.6 × 10 ⁻⁸ μm ² from FIG. Therefore, the minor axis is approximately 217.1 μm, and the major axis is approximately 325.7 μm. In this case, the distance between the cores can be 28.8 μm. Further, when the ratio of the area occupied by the core elements 10A, 10B, and 10C to the area surrounded by the outer periphery of the clad 21 is a core exclusive area ratio, the core exclusive area ratio is 47.3%.

FIG. 40 is a diagram illustrating a fifth example of the multi-core fiber according to the present embodiment. In this example, the multi-core fiber 2E has a clad 22 with a ratio e of 2.0, and three types of core elements 10A, 10B, and 10C are arranged in the clad 22. These core elements 10A, 10B, and 10C are arranged in a triangular lattice shape so that adjacent core elements are of different types. Further, in this example, when the number of core elements arranged along the major axis direction is counted in order along the minor axis direction, an array of 8-9-10-9-8 is obtained, and the core elements 10A, 10B, The total number of 10C is 45. In the multi-core fiber 2E of this example, the probability of breakage when the standard single mode fiber is bent at a bending diameter of 30 mm, assuming that the proof is 2%, the bending diameter is 30 mm, and the angle θ in the bending direction of the multi-core fiber is 45 degrees. The cross-sectional area when the fracture probability is the same as 2 × 10 ⁻⁶ is approximately 55.8 × 10 ⁻⁸ μm ² from FIG. Therefore, the minor axis is approximately 176.8 μm, and the major axis is approximately 353.6 μm. In this case, the distance between the cores can be 28.8 μm. Further, when the ratio of the area occupied by the core elements 10A, 10B, and 10C to the area surrounded by the outer periphery of the clad 21 is a core exclusive area ratio, the core exclusive area ratio is 52.5%.

  The ratio e of the clad 21 and the arrangement of the core elements 10A to 10C shown in the above example are merely examples, and the ratio e and the arrangement of the core elements 10A to 10C can be changed as appropriate.

  As described above, the multi-core fibers 2A to 2E of the present embodiment include a plurality of cores 11A to 11C arranged in a matrix and a single clad 22 surrounding each of the cores 11A to 11C. The outer shape of the clad 22 in a cross section perpendicular to the longitudinal direction is a race in which a pair of straight lines 22L connected to each other by a semicircular curve 22C and a ratio e between the minor axis a and the major axis b is 2.5 or less. The track shape. Two or more cores are arranged along the minor axis direction, and more cores are arranged along the minor axis direction along the minor axis direction. The multi-core fibers 2A to 2E are used by being bent in a direction of less than 45 degrees with respect to the minor axis direction.

  Accordingly, when the multi-core fibers 2A to 2E having the outer shape of the clad 22 having a racetrack shape are bent and used at less than 45 degrees with respect to the minor axis direction, as described above, when the fracture probability is the same, The cross-sectional areas of the multi-core fibers 2 </ b> A to 2 </ b> E whose clad outer shape is a racetrack shape can be larger than those of the multi-core fiber having a circular clad outer shape. Therefore, with such multi-core fibers 2A to 2E, more cores can be arranged while suppressing deterioration in long-term reliability.

  Next, it will be described that more cores can be arranged when the angle θ in the direction of bending the multi-core fiber is set to 0 degree.

  FIG. 41 is a diagram of the first embodiment showing that a large number of cores can be arranged in the multicore fiber in the second embodiment when the angle θ is 0 degree. In FIG. 41, the coating layer 30 is omitted. In FIG. 41, a multi-core fiber 101 having a circular cross-sectional shape of the clad, a multi-core fiber 2F having a cross-section of the clad having a racetrack shape and a ratio e of the short diameter a to the long diameter b of 2.0, and a cross-section of the clad. Is a racetrack shape, and a multi-core fiber 2G having a ratio e of the minor axis a to the major axis b of 2.5 is superimposed. That is, FIG. 41 shows a multi-core fiber 101 having a circular clad shape and multi-core fibers 2F and 2G having a racetrack-shaped clad whose minor axis is the same size as the clad diameter of the multi-core fiber 101. Yes.

  As described in the first embodiment, when the multi-core fiber is bent, the most stressed position is the position on the outermost peripheral side of the clad in the bent state. Therefore, when the multicore fibers 2F and 2G having such a cladding are bent at an angle θ from the minor axis direction of 0 degree, the magnitude of the stress at the most stressed position was bent with the same curvature. The magnitude of the stress at the most stressed position in the multi-core fiber 101 is the same. Therefore, when the multi-core fibers 2F and 2G are bent at an angle θ of 0 degrees as described above, the break probability of the multi-core fibers 2F and 2G is made equal to the break probability of the multi-core fiber 101 bent with the same curvature. For this reason, compared with the multi-core fiber 101, the multi-core fibers 2F and 2G can suppress deterioration in long-term reliability.

  In addition, as shown in FIG. 41, as compared with the multi-core fiber 101 having a circular cross-sectional outer shape, the clad minor axis a of the multi-core fibers 2F and 2G is the same as the clad diameter of the multi-core fiber 101 as described above. It is made a size. Therefore, the cross-sectional area of the clad of the multi-core fibers 2F and 2G is made larger than the cross-sectional area of the clad of the multi-core fiber 101. In the multi-core fibers 2F and 2G, a larger number of core elements than the number of core elements arranged along the minor axis direction are arranged along the major axis direction. Accordingly, the multi-core fibers 2F and 2G can have more core elements than the multi-core fiber 101 having the same diameter as the minor axis a of the clad of the multi-core fibers 2F and 2G.

  An example of the number of core elements that are specifically arranged will be shown. Similarly to the first embodiment, the core element that can be disposed in the clad of the multi-core fiber 101 is a core element that overlaps the broken line and a core element that is disposed inside the broken line, and is 37. In addition, the core elements that can be disposed in the clad of the multi-core fiber 2F are a core element that overlaps with a dotted line and a core element that is disposed inside the dotted line in FIG. Accordingly, the number of core elements included in the multi-core fiber 2F is 93. The number of core elements included in the multi-core fiber 2G is 117.

  FIG. 42 is a diagram of a second configuration showing that a large number of cores can be arranged in the multicore fiber in the second embodiment when the angle θ is 0 degree. In FIG. 42, the coating layer 30 is omitted. 42, the multi-core fiber 102 having a circular cross-sectional shape of the clad, the multi-core fiber 2H having a cross-section of the clad having a racetrack shape and a ratio e of the short diameter a to the long diameter b of 2.0, and a cross-section of the clad. Is a racetrack shape, and a multi-core fiber 2I having a ratio e between the minor axis a and the major axis b of 2.5 is superimposed. However, in this example, a multi-core fiber 102 having a circular clad shape and multi-core fibers 2H and 2I having a racetrack-shaped clad 22 in which the short axis a is smaller than the diameter of the clad of the multi-core fiber 102 are shown. .

  When the multi-core fibers 2H and 2I of this example are bent at an angle θ of 0 degrees from the minor axis direction, the distance between the straight lines 22L is smaller than the diameter of the clad of the multi-core fiber 102. Is smaller than the breaking probability of the multi-core fiber 102 bent with the same curvature. For this reason, the multi-core fibers 2H and 2I can suppress deterioration of long-term reliability as compared with the multi-core fiber 102.

  Further, as shown in FIG. 42, the multi-core fibers 2H and 2I have more core elements than the multi-core fiber 102, although the distance between the straight lines 22L is smaller than the diameter of the clad of the multi-core fiber 102. Can do.

  An example of the number of core elements that are specifically arranged will be shown. The core element that can be arranged in the clad of the multi-core fiber 102 is 37 as in the first embodiment. In FIG. 37, the core element that can be disposed in the clad of the multi-core fiber 2H is a core element that overlaps the dotted line and a core element that is disposed inside the dotted line, which is 93. The number of core elements included in the multi-core fiber 2I is 117.

  As described above, the multi-core fibers 2F to 2I of the present embodiment also have a cross-sectional outer shape that is circular as compared with the conventional multi-core fibers 101 and 102 as described with reference to FIGS. The deterioration of the fracture probability can be suppressed, and many cores can be arranged.

(Third embodiment)
Next, a third embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 1st Embodiment, or equivalent, except the case where it demonstrates especially, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 43 is a diagram showing the multi-core fiber tape of the present embodiment. A multi-core fiber tape 51 shown in FIG. 43 has a plurality of multi-core fibers 1A of the first embodiment arranged in parallel in a single tape layer 50. The tape layer 50 has a flat plate shape in which the parallel direction of the multi-core fibers 1A is thinned. Therefore, the multi-core fiber tape 51 is easily bent in the thickness direction. The multi-core fiber 1 </ b> A disposed in the tape layer 50 is disposed so that the minor axis direction is 30 degrees or less from the thickness direction of the tape layer 50. The tape layer 50 may be formed as a single tape layer 50 by molding a resin, or may be formed as a single tape layer 50 by bonding two tapes.

  As described above, the multi-core fiber tape 51 of the present embodiment includes the multi-core fiber 1A in which the outer shapes of the clads 21 arranged in parallel with each other are elliptical, and the single tape layer 50 that covers each multi-core fiber 1A. . And each multi-core fiber 1A is arrange | positioned so that a breadth direction may be 30 degrees or less with respect to the direction perpendicular | vertical to the parallel direction of multi-core fiber 1A, ie, the thickness direction. In such a multi-core fiber tape 51, when the tape is bent, each multi-core fiber 1A bends in a direction of 30 degrees or less with respect to the minor axis direction. Therefore, it is possible to suppress the deterioration probability of each multi-core fiber 1A from deteriorating. Further, more cores can be arranged by arranging a plurality of multi-core fibers 1A in parallel.

  In the present embodiment, the multi-core fiber tape 51 on which the multi-core fiber 1A is disposed has been described as an example. However, the multi-core fiber disposed on the multi-core fiber tape 51 of the present embodiment is the multi-core fiber described in the first embodiment. If there is no particular limitation.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described in detail with reference to FIG. In addition, about the component which is the same as that of 2nd Embodiment and 3rd Embodiment, or equivalent, unless otherwise demonstrated, the same referential mark is attached | subjected and the overlapping description is abbreviate | omitted.

  FIG. 44 is a diagram showing the multi-core fiber tape of the present embodiment. The multi-core fiber tape 52 shown in FIG. 44 has a plurality of multi-core fibers 2A of the second embodiment arranged in parallel in a single tape layer 50. The tape layer 50 has a flat plate shape in which the parallel direction of the multi-core fibers 2A is thinned. Therefore, the multi-core fiber tape 52 is easily bent in the thickness direction. The multi-core fibers 2 </ b> A disposed in the tape layer 50 are disposed such that the minor axis direction is less than 45 degrees from the thickness direction of the tape layer 50. In particular, the multi-core fiber 2 </ b> A is preferably arranged so that the minor axis direction is 44 degrees or less from the thickness direction of the tape layer 50. The multi-core fiber 2A is arranged such that the ratio e in the second embodiment is 2.0 or more and 2.5 or less, and the minor axis direction is 45 degrees or less from the thickness direction of the tape layer 50. It is preferable.

  As described above, the multi-core fiber tape 52 of the present embodiment includes the multi-core fiber 2A in which the outer shape of the clad 22 arranged in parallel with each other is a racetrack shape, and the single tape layer 50 covering each multi-core fiber 2A. Prepare. And each multi-core fiber 2A is arrange | positioned so that a minor axis direction may be less than 45 degree | times with respect to the direction perpendicular | vertical to the parallel direction of multi-core fiber 2A, ie, the thickness direction. In such a multi-core fiber tape 52, when the tape is bent, each multi-core fiber 2A bends in a direction of less than 45 degrees with respect to the minor axis direction. Therefore, it is possible to suppress the deterioration probability of each multi-core fiber 2A from deteriorating. Further, more cores can be arranged by arranging a plurality of multi-core fibers 2A in parallel.

  In the present embodiment, the multicore fiber tape 52 on which the multicore fiber 2A is disposed has been described as an example. However, the multicore fiber disposed on the multicore fiber tape 52 of the present embodiment is the multicore fiber described in the second embodiment. If there is no particular limitation.

  Although the multicore fiber and the multicore fiber tape of the present invention have been described above, the present invention is not limited to the above embodiment.

  For example, for the multi-core fiber in which the outer shape in the cross section perpendicular to the longitudinal direction of the cladding is a non-circular shape having the smallest diameter in the predetermined direction and having no recess, in the above embodiment, the elliptical shape and the racetrack are used. Although the shape has been described as an example, the present invention is not limited to this. FIG. 45 is a diagram showing another shape of the clad. As shown in FIG. 45, the clad 23 of this example is D-type. When the D-shaped minor axis direction is a predetermined direction, the fracture probability when bending in the predetermined direction is equivalent to the fracture probability of a multi-core fiber having a circular cross section having the same diameter as the minor axis shown in FIG. . Therefore, according to the multi-core fiber having such a clad, it is possible to arrange many cores while suppressing deterioration of long-term reliability.

  Generalizing this, the outer shape in the cross section perpendicular to the longitudinal direction of the clad has a non-circular shape with the smallest diameter in the predetermined direction and no recess, and two or more cores are formed along the predetermined direction. A multi-core fiber that is arranged and bent along a direction perpendicular to the predetermined direction, and more than the number of cores arranged along the predetermined direction, is bent in the predetermined direction to be used. . According to this multi-core fiber, it is possible to arrange many cores while suppressing deterioration of long-term reliability as described above.

  In addition, a multi-core fiber tape using such a multi-core fiber includes a plurality of the multi-core fibers arranged in parallel with each other and a single tape layer covering each multi-core fiber, and each multi-core fiber is a multi-core fiber. It is arranged so that a predetermined direction is oriented in a direction perpendicular to the fiber parallel direction. When this multi-core fiber tape is bent, each multi-core fiber bends in a predetermined direction. Therefore, it can suppress that the fracture probability of each multi-core fiber deteriorates. Further, a larger number of cores can be arranged by arranging a plurality of multi-core fibers in parallel.

  The multi-core fiber and multi-core fiber tape according to the present invention can arrange many cores while suppressing deterioration of long-term reliability, and can be used in the optical communication industry.

1A to 1E, 2A to 2E ... multi-core fiber 10A to 10C ... core element 11A to 11C ... core 12A to 12C ... inner cladding 13A to 13C ... low refractive index layer 21, 22, ...・ Clad 30 ... Coating layer 50 ... Tape layer 51,52 ... Multi-core fiber tape

Claims (8)

A plurality of cores arranged in a matrix, and
A single cladding surrounding each said core;
With
The outer shape in a cross section perpendicular to the longitudinal direction of the cladding is a non-circular shape having a diameter that is the smallest in a predetermined direction and does not have a recess,
Two or more cores are arranged along the predetermined direction, and more cores are arranged along the direction perpendicular to the predetermined direction than the number of the cores arranged along the predetermined direction. And
A multi-core fiber that is bent in the predetermined direction. The multi-core fiber according to claim 1, wherein the outer shape of the clad is a D-type. A plurality of cores arranged in a matrix, and
A single cladding surrounding each said core;
With
The outer shape of the cross section perpendicular to the longitudinal direction of the cladding is an elliptical shape with an ellipticity of 2.5 or less,
Two or more cores are arranged along the minor axis direction of the ellipse, and more cores than the cores arranged along the minor axis direction are arranged along the major axis direction of the ellipse. Arranged,
A multi-core fiber bent in a direction of 30 degrees or less with respect to the minor axis direction. A plurality of cores arranged in a matrix, and
A single cladding surrounding each said core;
With
The outer shape in a cross section perpendicular to the longitudinal direction of the cladding is a racetrack shape in which a ratio of a minor axis to a major axis is 2.5 or less, in which a pair of straight lines parallel to each other is connected by a semicircular curve,
Two or more cores are arranged along the minor axis direction of the racetrack shape, and the number is larger than the number of cores arranged along the minor axis direction along the major axis direction of the racetrack shape. Of the core is arranged,
A multi-core fiber bent in a direction of less than 45 degrees with respect to the minor axis direction. The multi-core fiber according to any one of claims 1 to 4, wherein the number of the plurality of cores is greater than 37. A plurality of multi-core fibers according to claim 1 or 2 parallel to each other;
A single tape layer covering each multi-core fiber;
With
Each of the multi-core fibers is arranged such that the predetermined direction is oriented in a direction perpendicular to a parallel direction of the multi-core fibers. A plurality of multi-core fibers according to claim 3 in parallel with each other;
A single tape layer covering each multi-core fiber;
With
Each of the multi-core fibers is arranged such that the minor axis direction is 30 degrees or less with respect to a direction perpendicular to the parallel direction of the multi-core fibers. A plurality of multi-core fibers according to claim 4 in parallel with each other;
A single tape layer covering each multi-core fiber;
With
Each of the multi-core fibers is arranged such that the minor axis direction is less than 45 degrees with respect to a direction perpendicular to the parallel direction of the multi-core fibers.

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